Aerobic step



FIG. 1 is a top perspective view of an aerobic step showing our new design;

FIG. 2 is a top view of the aerobic step of FIG. 1;

FIG. 3 is a first side view of the aerobic step of FIG. 1, the opposite side view being identical;

FIG. 4 is a second side view of the aerobic step of FIG. 1, the opposite side view being identical; and,

FIG. 5 is a bottom view of the aerobic step of FIG. 1.

The broken lines in FIG. 5 show portions of the aerobic step which form no part of the claimed design. 

CLAIM The ornamental design for an aerobic step, as shown and described. 